We investigated the participation of transmembrane proteins on the expression of chemically-homologous domains on the surface of mammalian cells. Conjugates of lectins and colloidal gold were employed to label intact, hypotonic-disrupted, and freeze-fractured membranes. The precise location of the lectin-gold label was analysed in situ by electron microscopy. To study the a regionalization of surface components, a highly polarized cell (the spermatazoon) was choosen as the first experimental model. Our results showed that: a) the large intramembrane particles seen on freeze-fracture faces of cells are the morphological counterpart of integral membrane sialo-proteins; b) the surface of flagella has a high density of transmembrane glycoproteins that may be involved in the transduction of movement from the cytoskeleton to surface exposed elements; c) lysosomal and plasma membrane may express unequal complements of fully glycosilated components.